Reintroducing species to their natural habitats

Covered from coast to coast in extensive woodlands and wetlands, the United Kingdom was once a biodiverse wildlife haven. Over the centuries, however, the UK’s natural habitats have been in decline and just small pockets of many species’ historical ranges remain. Recently there has been a concerted effort to restore natural habitats in the UK and there are many projects focused on setting species on the path to recovery, hopefully reversing this decline.

Often when an area is being restored to its former natural state, the animals and plants that used to thrive need a little bit of help to return. The reintroduction of species provides a way to stabilise or re-establish populations that have suffered a decline, increasing the population to a sustainable level. Individuals that have been reared in captivity, rehabilitated from illness or injury, or moved from areas of abundance are released into their natural habitats where they previously occurred.

Each reintroduction needs to be carefully considered. Are the conditions suitable for the species to flourish and for the population to become self-sustaining? What impacts might they have on the rest of the ecosystem to which they are being introduced?

Here are some examples of animals and plants that have been reintroduced to the UK:

Beaver

There are two species of beaver - the Eurasian beaver and the American beaver. The Eurasian beaver was once widespread throughout the UK, but just over 400 years ago, this species was wiped out due to a loss of suitable wetland habitat and as a result of overhunting for its meat, fur, and castoreum - a substance all beavers produce and use to waterproof themselves.

The Eurasian beaver is well-adapted to fulfil its role as a vital engineer of wetland habitats, with a broad torso and widely spaced, stubby legs which are ideal for building dams, and large, well-developed incisors which are efficient at gnawing the wood required for this construction. The Eurasian beaver is also able to close its nose and ears while underwater, and has a transparent second eyelid, known as a nictitating membrane, which helps it to see underwater. Furthermore, inner lips directly behind its teeth allow the beaver to use its teeth underwater to gnaw tree limbs without flooding its mouth with water.

The Eurasian beaver is recognised as a ‘keystone species’ due to its role in maintaining the structure of its ecosystem. By constructing dams, the beaver creates new ponds and lakes, allowing many other animals and plants to colonise these areas and take advantage of the new habitat. Beaver activity is also especially good at controlling the flow of water - retaining water upstream. The reintroduction of beavers is one potential solution to a problem that is widespread across the UK today - flooding.

A combination of conservation measures (including hunting restrictions and habitat protection) and reintroductions has resulted in the beaver returning to much of its former range across Europe, and a number of its populations are rapidly expanding. In the UK there have been a number of trial (and accidental) reintroductions of beavers:

Scotland

A five year study was run in Scotland from May 2009 to explore whether beavers could enhance and restore natural environments. The scientific monitoring came to an end in May 2014, and on 24 November 2016 the Scottish Government made the landmark announcement that the beaver is to be formally recognised as a native species, and will remain in Scotland. The project will now reinforce the existing population in Knapdale, Argyll, and the established population on the River Tay will be allowed to remain in place.

England

Two families of beavers were released during the Ham Fen Beaver Project in Kent in 2001 to try to maintain the habitat. Using machinery was proving very costly and impossible for some areas, and beavers were thought to be the solution. The released beavers were enclosed by a fence to prevent them from expanding their range. The beavers, and the habitat, are now thriving.

In March 2011, a breeding pair of beavers were released into an enclosure on an estate in Devon. The effect of the pair on the site has been astounding as the beavers have transformed what was a small trickle of water into an amazing series of waterways. The project is continuing and researchers are monitoring the ecological effects the beavers are having on their environment.

In 2014 there were sightings of beavers on the River Otter in east Devon, but no one is quite sure how they got there. In June 2015, the first wild baby beavers were spotted on the river.

Wales

A couple of sites have also been identified in Wales for the possible reintroduction of beavers, but this project is still in the initial stages of planning.

Pine marten

Pine martens were once found throughout most of Britain but habitat loss, persecution by gamekeepers and hunting for fur have all contributed to the decline of the species. Human disturbance is still a key threat to pine martens, as well as consumption of poison intended to kill foxes and crows and being shot for attacking chickens or being mistaken for mink.

Active at dusk and during the night, the pine marten has a broad diet that varies throughout the year depending on availability. Small rodents, birds, beetles, carrion and eggs are all eaten, and berries are very important in the autumn. They are adept climbers, but tend to hunt on the ground.

Although found throughout most of central and northern Europe the UK range of the pine marten, until recently, was mostly restricted to the Scottish Highlands and Grampian. Although a few populations did occur in southern Scotland and Northern Ireland, the pine marten was mostly extinct throughout most of England and Wales, with only a few scattered populations.

However, conservation management in areas where the pine marten persists is helping the species. In 2014, the Vincent Wildlife Trust (VWT) launched its Pine Marten Recovery Project which saw the translocation of pine martens from Scotland to restore a healthy population in the rural landscape of Wales. The first step was completed in autumn 2015, with the translocation of 20 pine martens, and the first Welsh-born pine marten kits arrived in early summer 2016.

Red kite

Formerly a common and widespread bird, the red kite was locally extinct in England and Scotland by 1900, and only a remnant population survived in central Wales. Today, the range of the red kite is expanding in the UK and successful reintroductions have allowed the bird to re-colonise several parts of its former range. Overall population numbers are now increasing in several areas of England.

The red kite has been described as 'the most beautiful bird of prey in Britain'. Its plumage is a wonderful mixture of black, chestnut, grey and reddish-brown and the underwings have an obvious white patch which strongly contrasts with jet-black wing-tips. In flight the red kite's most notable feature is its long, deeply forked tail. The wing-tips are strongly 'fingered' and the bird's soaring flight is one of the most graceful sights in the British countryside.

It had long been hoped that red kites would find their way back to England naturally as their numbers increased in Wales. However, the Welsh population had been slow to increase and expand its range due to the low level of breeding success and reluctance for birds to breed far from the nest site where they themselves were reared. To improve the fortunes of the red kite a decision was made to try to reintroduce them to suitable areas in England and Scotland. English Nature, Scottish Natural Heritage and the RSPB began a project in 1989 using nestlings brought in from Spain and southern Sweden. The young birds were kept in captivity for six to eight weeks with minimal human contact, before being released into the wild.

Over a period of 5 years, 186 young red kites were released in the Chilterns of southern England and in northern Scotland and self-sustaining breeding populations have now become established in both areas. Further projects in England have resulted in breeding populations becoming established in the East Midlands and Yorkshire.

In the year 2000, a breeding survey recorded 16 pairs in the Midlands, 3 pairs in Yorkshire, and well over 100 pairs in the initial release area in the Chilterns. However, although highly successful in England, the reintroductions in Scotland have not seen similar results as numerous incidents of illegal poisoning appear to be preventing the reintroduced population from successfully rearing young and the population remains at around 35 breeding pairs. The RSPB is working with police wildlife crime officers to try to track down those responsible and stop this persecution.

White-tailed eagle

The white-tailed eagle became extinct in the UK in 1916 following excessive shooting, but 82 young birds from Norwegian nests were reintroduced from 1975 to the Island of Rhum in the Inner Hebrides of Scotland. The first chick from these birds successfully fledged in 1985. However, because individuals of this species only breed when they are 5 or 6 years old, and they then may only have one chick every two years, the increase in the population was slow. The population was therefore supplemented between 1993 and 1998 with the reintroduction of an additional 58 young eagles from Norway.

This re-established population is now thought to be growing, and has plenty of suitable habitat to expand into. Reintroductions are now also taking place in east Scotland, and these individuals are also now breeding.

Common crane

The common crane has been wiped out in much of southern and western Europe over the past few centuries. The main threat to this species came from habitat loss and degradation as a result of dam construction, urbanisation, agricultural expansion, and drainage of wetlands. Although it adapted to human settlement in many areas, nest disturbance, continuing changes in land use, and collision with electricity lines still caused problems, and further threats included persecution due to crop damage, pesticide poisoning, egg collection, and hunting.

With the protection and restoration of suitable wetland habitats, the common crane has started to return to many of its former breeding grounds, and reintroductions have given the cranes a helping hand. The Great Crane Project has hand-reared common crane chicks, and released them in the Somerset Levels and Moors with the aim of re-establishing a wild breeding population. The project aims to establish around 20 breeding pairs in south-western England by 2025 and, with 16 breeding pairs in 2015, looks set to reach if not exceed this target.

Sand lizard

The principal reason for the decline of the sand lizard is the massive loss of its habitat. During the 20th century, in north-western Europe and the UK, large areas of heath were removed for development or agriculture. Most of the surviving populations were fragmented, and surrounded by conifer plantations or built land, causing numerous ecological issues such as inbreeding and pressure on resources. Heathland is also highly susceptible to fire and damage through recreational use.

The sand lizard is Britain's only egg-laying lizard and has an attractive pattern of dark spots with light centres, over a background of brown or grey. During the breeding season between April and May, the sides of the male’s body become bright green. Britain marks the north-western limit of the sand lizard's range, and it is now found naturally only on scattered sites.

Efforts to increase the populations of this attractive reptile include the protection of existing sites, management and re-creation of heathland and dunes suitable for the lizards, and reintroduction of animals to specially prepared sites within their known or presumed former range. In the wild, only around five percent of eggs laid will survive to become adults. This can be due to inclement weather, predation or disturbance. Adults that do survive are unable to cross unsuitable habitat in order to colonise new areas, so the reintroduction of captive-reared young is an effective conservation solution.

A 3-year reintroduction project released 9,000 captive-bred sand lizards into suitable dune and heathland sites in England and Wales and a total of 76 reintroductions had taken place by 2012. It was estimated that 65 percent of the reintroductions had been successful, resulting in a re-established population. There are three ‘races’ of sand lizard in the UK and it was important that these races were represented in the release of captive-bred animals. The sand lizard has now been reintroduced to 11 counties in the UK, returning the species to 7 counties where it had become locally extinct.

Natterjack toad

The UK marks the western edge of the natterjack toad’s range, and its distribution is patchy in the area. Loss of habitat and the drying up of suitable ponds has contributed to its decline and this toad is now severely threatened across much of its European range. In the UK the largest concentration of natterjack toads was in the northwest coast of England with the species being naturally restricted to three main habitat types: costal dune systems, upper saltmarsh and lowland heath - places characterised by light, sandy soils and warm, shallow ponds, often near the coast. Natterjacks occur in southwest Ireland where they are the only native toad.

The chief distinguishing feature of the natterjack toad is the yellow stripe down its back. Shorter hind legs also tell the natterjack toad apart from the common toad and it has a tendency to run instead of hopping or walking, which is why it is sometimes called the ‘running toad’.

The natterjack toad was the subject of a Biodiversity Species Action Plan and most of their UK sites are now protected, some as nature reserves. Through English Nature's Species Recovery Programme, work focused on maintaining suitable ponds and, where possible, constructing new ones. New ponds must share the characteristics of naturally occurring ones. They must be shallow in order to warm up swiftly during the day and have gently sloping sides to enable the adults and toadlets to climb out. Reintroduction programmes have also begun in order to conserve this unusual amphibian.

In the 1980s, conservationists began a programme to reintroduce the species to areas of remaining heathland. This rare species is now going from strength to strength at the sites of reintroduction. Natterjack toads are fully protected by law in the UK and it is illegal to capture, kill, disturb or injure the animals or to destroy or damage their breeding sites or resting places.

Large blue butterfly

The large blue butterfly became extinct in the UK in 1979, but has since been reintroduced through a long-term and highly successful conservation programme. This primary reason for the decline of this species was habitat loss, and a lack of research meant that the life cycle was not fully understood until after it had been lost from Britain. This butterfly relies on a certain species of ant in order to complete its life cycle, and this ant requires a habitat which has few tall plants, is well-grazed and where the surface temperature of the ground is warm. The loss of this habitat in many areas led to a drastic reduction in ant numbers and this, coupled with a major reduction in the populations of wild thyme, on which the female large blue butterfly lays its eggs, led to local extinction.

A co-ordinated approach toward conserving the large blue butterfly began in 1962 when a joint committee was formed. The committee was successful in finding colonies of butterflies but failed to discover any information concerning the relationship with the ant or the decline in ant numbers. The large blue butterfly was declared extinct in Britain in 1979. A decision was made to attempt reintroduction of the species and the butterfly was given special protection in 1975. In 1983 a reintroduction programme began with the importing of wild individuals from Sweden.

Even more butterflies were brought over in 1986 and in 1991 a five year recovery project was launched. So far suitable habitats have been re-created on all the earmarked sites and the large blue butterfly has been successfully reintroduced to several of them. As a bonus a significant increase in the numbers of another species of butterfly, the small pearl-bordered fritillary, have also been recorded. The large blue butterfly is now thriving, with highest numbers recorded for 80 years in 2016.

Short-haired bumblebee

Shrill carder bee (Bombus sylvarum)

Two species of bumblebee have become extinct in the UK over the last 80 years, the short-haired bumblebee and Cullem’s bumblebee, and more have become increasingly rare. The Short-haired Bumblebee Project formed in 2009 to try to recreate the flower-rich grasslands in southeast England where researchers could begin a reintroduction programme.

Interestingly, the project first thought to reintroduce bees from New Zealand, as the bees there are directly descended from ones that were introduced from the UK over 130 years ago. However, after studying their genes it was discovered that the population was inbred and therefore unsuitable for reintroduction to the UK. The population in Sweden, however, was increasing and so in 2012, queen bees were moved from Sweden to the UK. Working extensively with farmers and land owners, the project area consisted of over 8.5 square kilometres of flower-rich habitat, with the project providing advice on buying seeds, sowing, management and habitat maintenance.

In 2016, for the 4th year running, short-haired bumblebee workers have been recorded around the study area, with other previously rare species also making a comeback. Populations of the shrill carder bee, Bombus sylvarum, have returned to the area after a 25 year absence and the large garden bumblebee, Bombus ruderatus, after a ten year absence.

Lady’s slipper orchid

The lady's slipper orchid is Britain's rarest and most impressive orchid. The exotic looking flowers have claret petals that frame a beautiful bright yellow pouch. Thought to be one of the slowest-growing plants in the world, the lady's slipper orchid takes between 6 and 11 years of growth before it produces flowers.

In the UK, this orchid once had a widespread but localised distribution in northern England. Although this species was never common, it suffered a severe decline in the 19th century due to over-collection and at one point there was just a single wild flowering plant in the UK. After several years of protection, the wild plant recovered and started to flower again. These flowers were hand-pollinated, and the resulting seeds were sent to Kew Gardens.

The seeds are tiny, dust-like particles that contain no food reserves. The materials needed for germination are derived from a symbiotic relationship with a fungus. Orchids can be difficult to grow in artificial conditions for this reason, but the lady's slipper orchid has been extensively studied and successful ex-situ growth techniques have been devised, which have enabled it to be grown successfully and then reintroduced to the wild.

Kew and Natural England are working together to reintroduce seedlings into locations where the species died out. Some reintroduced plants have flowered and in 2009, seed pods formed after natural pollination by insects.

Reintroduction vs invasion

Reintroducing native species to their former range is very different from the introduction of species to somewhere that they have never previously been found. This can be very harmful to native species.

Glossary

Measures to conserve a species that occur outside of the natural range or habitat of the species. For example, in zoos or botanical gardens.

Germination

The beginning of growth, usually following a period of dormancy and in response to favourable conditions. For example, the sprouting of a seedling from a seed.

Heath

Area of open, uncultivated land, usually dominated by dwarf shrubs on acid, free-draining soils.

Heathland

Area of open, uncultivated land, usually dominated by lime-hating dwarf shrubs on acid, free-draining soils.

Inbreeding

The breeding of closely related individuals. An inbred population usually has less genetic variability and this is generally disadvantageous for its long-term survival and success.

Nictitating membrane

A thin, tough, transparent or translucent membrane, or ‘inner eyelid’, found in various species of birds, reptiles, amphibians and fish, but less common in mammals. The nictitating membrane can be drawn across the eye to protect it from damage, or to moisten the eye while maintaining vision.

Pollination

The transfer of pollen grains from the stamen (male part of a flower) to the stigma (female part of a flower) of a flowering plant. This usually leads to fertilisation, the development of seeds and, eventually, a new plant.

Symbiotic

Describes a relationship in which two organisms form a close association. The term is now usually used only for associations that benefit both organisms (a mutualism).

Translocation

When individual living organisms from one area are transferred and released or planted in another area.